1. Field of the Invention
The present invention relates to a shutter unit, a shutter unit with a built-in lens, and an imaging apparatus.
2. Description of the Related Art
There have been built-in camera modules for imaging apparatuses, such as a camera-equipped cellular phone, a digital camera, etc., that are equipped with a mechanical shutter unit that regulates the quantity of light reaching photo elements of a charge-coupled device (CCD) by opening or shutting sectors (shutter blades). These types of shutter units frequently employ an actuator that opens or shuts sectors connected to a rotor by rotating the rotor using a magnetic force generated by exciting a yoke by the supply of electricity to a coil located in the middle of the yoke such as that described in Japanese Patent Application Laid-Open Publication No. s60-235125.
In FIGS. 23 and 24 an example of a shutter unit based on conventional techniques is shown.
A shutter unit 1700 includes a base plate 1710, and an actuating unit 1720 that is composed of a coil 1721 and a yoke 1722 that is excited by electrical supply to the coil 1721 is disposed on a surface 1710A formed on the object side of a base plate 1710 along the direction of an optical axis 1700A.
A rotor 1730 is disposed so as to penetrate the base plate 1710 from the surface 1710A of the base plate 1710 to the opposite surface (imaging plane side) along the direction of the optical axis 1700A such that the rotor 1730 can rotate freely. The cylindrical surface of the rotor 1730 is magnetized by a dipole permanent magnet. The coil 1721, the yoke 1722, and the rotor 1730 are enclosed by a partition plate 1740 that retains the rotor 1730 as a bearing.
Inside the base plate 1710, sectors (not illustrated) coupled with the rotating motion of the rotor 1730 are disposed to open and shut the opening 1710B formed on the base plate 1710. The base plate has a depression 1710C, that has an internal diameter larger than that of the opening 1710B, to set a lens unit 1900 that is shown in FIGS. 25 and 26.
At the rotor unit 1730 of the shutter unit 1700, a magnetic force (attractive force) in a predetermined direction is generated by the excitation of the yoke 1722 with an electrical supply to the coil 1721. The rotor 1730 thus rotates in the predetermined direction. The opening 1710B is opened or shut by the sectors coupled with the rotating motion of the rotor 1730.
As shown in FIG. 23, the yoke 1722 has a substantially U-shaped to enable, when disposed on the base plate, the rotor 1730 to be located between the two ends of the yoke 1722 and to enable the coil 1721 to be arranged in the middle, and to avoid the interference of a lens frame 1910D of the lens unit 1900 when the shutter unit 1700 and the lens unit 1900 are assembled and integrated.
The size of the shutter unit 1700 is minimized as far as practicable by the arrangement of the yoke 1722 and the coil 1721 having sufficient space from the lens frame 1910D on the base plate 1710 so that the yoke 1722 and the coil 1721 do not interfere with the lens frame 1910D. The outer dimensions of the shutter unit 1700 orthogonal to the direction of the optical axis 1700A (width) is denoted as W3.
FIGS. 25 and 26 are schematics of a conventional lens unit. A lens unit 1900 equipped with a base plate 1910 is integrated with the shutter unit 1700, and a cylindrical lens frame 1910D having a circular opening 1910C that is coaxial with the optical axis 1700A is formed on a surface 1910A on the object side of the base plate 1910 along the direction of the optical axis 1700A so that the cylindrical lens frame 1910D projects from the surface 1910A. Inside the opening 1910C formed in the lens frame 1910D, a lens cluster 1920 composed of lenses 1921 and 1922 is disposed.
FIG. 27 is a schematic of the shutter unit 1700 and the lens unit 1900 that are integrated. The shutter unit 1700 and the lens unit are assembled separately in individual manufacturing processes. As shown in FIG. 27, the shutter unit 1700 and the lens unit 1900 are assembled and integrated so that the surface 1710A of the shutter unit 1700 contacts the surface 1910B of the lens unit 1900, and so that the lens 1922 installed in the lens unit 1900 is partially accommodated in the space 1710C formed in the shutter unit 1700.
A shutter installed in the shutter unit 1700 has two shutter blades (sectors), and when the sectors are in a closed position, the sectors shut an opening that is coaxial with an optical axis by overlapping each other leaving a gap equivalent with their thickness. These sectors contact a surface of the case of the shutter unit 1700, and therefore, they move (slide) as they rub the surface in the motion of opening and shutting. There is a configuration to reduce the sliding friction generated when the sectors move by adding, inside the shutter unit, suitably shaped slide guides that contact the sectors such as that described in Japanese Patent Application Laid-Open Publication No. H8-152667). In addition, there is a configuration that includes light shields that prevent the leakage of light to the opening from the gap between two sectors as well as reduce sliding friction such as that described in Japanese Patent Application Laid-Open Publication No. 2002-14387, and a configuration that includes light shields to prevent light from penetrating to the optical axis from the periphery of two plates constituting a blade chamber to accommodate the sectors such as that described in Japanese Patent Application Laid-Open Publication No. 2002-107793.
In the conventional techniques above, however, a substantially U-shaped yoke that allows both an arrangement of a rotor and an attachment of a coil between the two ends of the yoke is commonly employed. In case the substantially U-shaped yoke is employed for a shutter unit, sufficient space must be secured to arrange the yoke and coil in a position outside of the optical axis, and therefore, the difficulty of shutter unit downsizing has been a problem.
With regard to a shutter unit described in Japanese Patent Application Laid-Open Publication No. 60-235125, although configuration allows downsizing upon integrating a shutter unit 1700 and a lens unit 1900, making the outer dimensions of the shutter unit along the direction of an optical axis 1700A (thickness) of W4, there has been a problem that the downsizing of the outer dimensions of the shutter unit along the direction of the optical axis 1700A is not easy as long as the shutter unit configuration described above is employed.
In order to solve the problem, consideration has been given to the installation of a lens and a shutter to a lens frame of a lens unit and a shutter unit that have been integrated. The diameter of the lens housing portion (diameter along the direction orthogonal to an optical axis) of the integrated lens frame must be slightly larger than lens diameter as a lens is required to be aligned. Thus, the opening of the lens frame to insert the lens needs to be formed larger proportionally to the housing diameter. In case sectors are arranged on the opening side of the lens frame, a problem arises in that the opening diameter becomes larger than the desired aperture diameter. Thus, a desired aperture diameter cannot be obtained whereas downsizing (thickness W4) can be realized by integrating a lens unit and a shutter unit into a single lens frame.
The downsizing of a sector portion, i.e., outer dimension orthogonal to the direction of an optical axis C (width and length), is also limited. The yoke that constitutes a part of a drive mechanism to open and shut sectors is formed in a shape that can accommodate a rotor between the two ends of the yoke. A substantially U-shaped is common for attaching the coil. In case of such a substantially U-shaped yoke, the downsizing of a shutter unit has been difficult as the width and length of a lens frame become large due to the securing of sufficient space to arrange a yoke and a coil in the position away from an optical axis.
In recent years, the downsizing of a shutter unit has been a particular problem for the development of camera modules in the background that compact camera modules are desired with progressing downsizing of camera phones and digital cameras.